The worst of the unparalleled fire risk faced by NSW has been averted as it emerged an army explosives exercise started the state's biggest blaze which has threatened thousands of homes and lives for a week.
The Rural Fire Service (RFS) said an investigation had found the Department of Defence training exercise on army land at Marrangaroo on October 16 caused the massive State Mine blaze near Lithgow which has burnt out more than 46,000 hectares of bushland and sparked fears of turning into a "mega-fire".
"The investigation has concluded the fire started as a result of exploding ordinances on the range on (last) Wednesday," a RFS spokesman said.
Defence said in a statement late on Wednesday is was "aware the NSW Rural Fire Service is of the view" the State Mine Fire was caused by a live ordnance exercise at Marangaroo and repeated it was still conducting its own investigation.
Blue Mountains mayor Mark Greenhill was "not happy at all" about the source of the fire which has destroyed three homes.
"I would have hoped on a day like that which was a dry day, a hot day, with the winds - the Australian military would have known it wasn't a good time to be igniting," he said.
"The fire has caused great concern to my community, it's done damage to my community and it just shouldn't have happened."
After the anticipated dire conditions of high winds and temperatures in the mid 30s arrived in the Blue Mountains and the Hunter region on Wednesday, RFS commissioner Shane Fitzsimmons said high risk strategies from firefighters had paid off.
"We have seen today, and indeed building throughout the week, one of the most significant threats to the Blue Mountains and Hawkesbury communities that is unparalleled," he said.
But, late on Wednesday afternoon, he followed that with words the hundreds of Blue Mountains residents who had left their homes had been hoping to hear.
"It would be safe to head back home tonight because the risk has been averted," he said.
Three fires - Springwood, Gateshead and Minmi - were on emergency alert during the day but all had been downgraded to watch and act by mid evening.
As of 6pm on Wednesday, there were still 73 fires burning in NSW and 29 uncontained blazes, but no further loss to property.
Mr Fitzsimmons said the Gateshead fire was burning right through the middle of the two towns it had initially threatened - Redhead and Dudley.
As conditions eased on Wednesday afternoon, the major blaze at Minmi that closed the M1 near Newcastle and caused the evacuation of two schools was downgraded to watch and act.
The Springwood blaze in the Blue Mountains, which last week destroyed nearly 200 homes, had showered more homes with embers as strong winds sprang up earlier on Wednesday.
Mr Fitzsimmons said he was surprised backburning in the Blue Mountains had held out in the extreme fire conditions.
Authorities are preparing for a south westerly change on Thursday that will bring lower temperatures but could still pose a risk to some communities.
"It has the very real potential to present new challenges and particularly in the northern end of the Winmalee Springwood fire where you could see ... that fire could pose threats tomorrow to communities in the Yarramundi Valley area and communities up through Grose Valley and communities to the north east," Mr Fitzsimmons said.
He warned there was still a lot of difficult and dangerous firefighting ahead, possibly for weeks.
Premier Barry O'Farrell lauded the "magnificent planning and preparation" of the emergency services which helped avert the worst.
While the risk was averted, fire activity throughout the day instilled fear in many communities.
Minmi Hotel kitchen manager and chef Sharon Wilson was holed up inside the hotel waiting for instructions from firefighters during the day.
"We've been spraying the pub down and the grass around it," she told AAP.
"There's a lot of embers and ash flying over us."
Two schools were also evacuated in the Minmi area.
Springwood resident Rae Tebbutt said the atmosphere in the normally carefree community was tense.
"Everyone is terrified. I've got three friends who have lost everything," she told AAP.After all schools in the Blue Mountains were closed on Wednesday, only a select few will be closed on Thursday.